Orb Weaving Spiders

146 American Entomologist Fall 2010

In late October, 2009, the managers of the Back River Wastewater

Treatment Plant in Baltimore, MD sought assistance in mitigating what they described as an extreme spider situation in their

2) under a single roof but with no side walls, had been proneworse than normal, and the facilitys maintenance and operations

personnel had voiced concerns over the potential risk of bites.

As an interagency team with expertise in arachnology, urban

entomology, and structural pest management, we were unprepared

for the sheer scale of the spider population and the extraordinary

blanketed much of the facilitys cavernous interior. Far greater in

the visual impact of the spectacle was nothing less than astonishing.

In places where the plant workers had swept aside the webbing to

This report has three objectives: 1) to document the phenomenon,

providing photographs, species determinations, and estimates of the

2) to compare this remarkable concentration of normally solitary

potential research utility of aquacentric structures such as sewage

treatment plants as readily accessible culturing facilities for predictable, dense aggregations of these spiders.

Materials and MethodsStudy Site. The Back River Wastewater Treatment Plant is

owned and operated by the City of Baltimore and is situated on the

west shore of Back River, a tributary of the Chesapeake Bay. Its sand

process by trapping the remaining suspended particles from the

sides of the facility are nearly identical, and are each covered with a

axis of the structure. Whereas the average height of the side roofs is

primary purpose of designing the facility with a roof was simply to

minimize algal growth in the sand beds, which would decrease their

Web Samples. The two principal types of webbing throughout

An Immense Concentration of Orb-Weaving Spiders With Communal Webbing in a Man-Made Structural Habitat

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(Arachnida: Araneae: Tetragnathidae, Araneidae)

Albert Greene, Jonathan A. Coddington, Nancy L. Breisch,Dana M. De Roche, and Benedict B. Pagac Jr.

American Entomologist 147

mensional mass) and laminar (a thin, dense sheet), and are described

in more detail in the text. Observations, photography, and collection

cut with a pole pruner saw from the nearly continuous sheet of silk

below the ceiling of the side roofs (Fig. 2). Four of the samples were

from the facilitys west side, and eight were from the east side. The

both sets of samples in order to yield the most conservative values

for spider densities.)

throughout the facility, three on either side of the central corridor.

Each sample consisted of a 2.0 m length of column, starting at the

.

All webbing samples were bagged and refrigerated, and their

spider occupants were extracted by hand and preserved in 70%

Estimation of Total Web Area, Volume, and Spider Population. various repeating architectural units, rough estimates of the total

extent of laminar and volumetric webbing throughout the building,

and then extrapolating from the species composition within the analyzed web samples. Both architects drawings provided by the plant

to derive the percentages of these components that were covered or

of the assumptions and limitations of the estimation process.

Following are the architectural units used to establish the webbing estimates:

Ceiling Above Sand Beds.2. In calculating the amount ofsets of trolley beam hangers (described below), a separate structural

component that formed the supports for the facilitys most conspicuous masses of volumetric webbing. The area of each rectangular

2. Without them, the2.

Roof Support Columns. The buildings roof is supported by 27and the innermost columns that support the central corridors roof

ones vary due to the sloping side roofs

the innermost ones are much taller, with

a height of 7.11 m.

Trolley Beam Hangers. The trolleybeam hangers are rows of rectangular

steel frames, fastened to the roof purlins

between every other sand bed, that support the horizontal beams holding the

sliding loops of electrical cables for the

traveling bridges. Each side of the facil

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process are located between every other sand bed, totaling 12 on

7), including the catwalk grate openings.

Traveling Bridges. Each sand bed is serviced by a travelingbridge containing a backwash pump that pulls up the entrapped

solids as the structure slowly moves on side rails over the bed. The

Railings. The extensive safety rails in the facility served aswebbing frameworks throughout much of their lengths (Fig. 9). Six

buildings long axis: one on either side of the central corridor and one

on either side of the narrow walkway on both outer edges. Although

the inner railings had gaps to allow access to the transverse catwalks,

they are treated as continuous lengths because the spiders readily

webbed across them. In addition, each of the traveling bridges had

Electrical Conduits. Two parallel tracks of electrical conduit

run along either side of the central corridor and served as webbing

frameworks in the same manner as the safety rails. Each set of

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Fig. 6. &ORVHXSRIWUROOH\EHDPKDQJHUZHEELQJ7KHEODFNspecks are PDLQO\LQGLYLG-XDOVRIERWKT. guatemalen-sis and L. sclopetarius.

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ResultsWebbing. The most distinctive manifestation of the spider

of webbing that obscured about 70% of the ceiling on either side of

the central corridor, a mostly unbroken expanse of relatively dense,

2. The sheet was anchored principally to the purlins(horizontal roof supports running the long axis of the building) and

rafters (larger, transverse beams that support the purlins), rather

than to the underside of the roof itself. On 29 October, when A.G.

their narrow attachment points (Fig. 10), primarily toward the edges

of the building due to wind from a recent storm.

Similarly, what had apparently been more extensive laminar

webbing across the central corridor ceiling earlier in the season had

undergone cycles of sectional fraying and reattachment, so that in

places the silk sheets resembled wash hanging on lines in an alley

(Fig. 11). Measured directly, the combined area of these remnants

was approximately 191.0 m2. Together with the main horizontal

expanses under the side roofs, the total laminar webbing in the

2.However, the majority of webbing throughout the facility was

. Table 1 lists the various architectural units that had been used as

supports for these masses of tangled silk strands, and the estimated

the immediate visual spectacle of the phenomenon. In contrast, the

sight beneath grated catwalks.

Despite being abundantly occupied

withspiders, thewebbinginmost locations was dense enough to catch most

catwalks, and other lower surfaces

largely free of this material. Although

much of the volumetric silk had the

same seemingly haphazard structure

of cobweb, these networksparticularly the more extensive and readily

visible ones supported by the trolley

beam hangers, traveling bridges, and

railingsnevertheless also displayed

partial orb webs could occasionally be

discerned amidst the sparser tangles,

particularly where Larinioides wasmore abundant.

Although, for the sake of convenience, the calculations of webbing

dimensions assumed a strict spatial

Table 1. Architectural Elements Used to Estimate Total Amount of Volumetric Webbing in Back River Sand Filtration Facility.

Estimated

Volume units volume occupied webbing(m) by webbing volume (m)

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discontinuity between laminar and volumetric production, their

boundaries in reality were usually imprecise. For example, the

part of the central corridor ceilings laminar total, even though its

addition, the various units of volumetric silk typically extended beyond the structural frameworks used to calculate their volume (Fig.

the building, often with extensive bridging between our arbitrarily

delineated categories. For these reasons, our estimates of its total

extent are markedly conservative and represent what we regard as

minimum values.

All webbing decreased to some extent toward the facilitys exbuilding was considerable. Both laminar and volumetric silk had

become tattered and fragmented in virtually every location, supporting the plant managers observations that the webbing recorded on

the sampling date was almost entirely the result of a single seasons

work. However, web construction in the facility continued at a low

level throughout the winter. On 22 February 2010, small amounts

of fresh silk in the form of accumulated drag lines and tangled

volumetric webbing, often with a strong laminar component, were

locally conspicuous on posts, railings, and cavities in equipment,

all in association with adult female Larinioides that were shelteringnearby (see following section).

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Table 2. Numbers of spiders collected in webbing samples from Back River Sand Filtration Facility.

Family Species Juveniles Total

Araneidae Larinioides sclopetarius Mangora sp. 1 1

Dictynidae Dictyna bellans Gnaphosidae Gnaphosidae sp. 1 1Salticidae Sitticus fasciger Tetragnathidae Tetragnatha guatemalensis

T. guatemalensis Theridiidae Parasteatoda tepidariorum

Steatoda grossa (C. L. Koch) 1 1Steatoda triangulosa ( Theridiidae sp. 2 2

Spiders. hatchlings, were extracted from the web samples. Although 9 genera

entirely the product of two hyperabundant species, Tetragnatha guatemalensisLarinioides sclopetarius T.guatemalensis, further contributing to the pronounced dominanceof this species at the site. Since these tiny spiderlings began actively

dispersing as soon as the web samples were removed from their

bags, many escaped capture and their actual number substantially

exceeded our total. In fact, the aggregation as a whole at the time

of sampling was overwhelmingly one of immatures. Even if the

specimens, with the percentages for the two principal species virtu T. guatemalensis L. sclopetarius). This extremely close similarity was repeated with the sex of the adult

T. guatemalensis andL. sclopetarius (Table 2).

As might be expected, the spider populations were not uniformly

distributed throughout the facility, but displayed considerable

and column samples. Of the four principal species, densities of

T. guatemalensis, L. sclopetarius, and Parasteatoda tepidariorum (C. L. Koch) were far greater in the volumetric web T. guatemalensisto the females tendency to deposit their egg sacs above the areas

of greatest spider activity. Although many of the sacs were in the

sheet itself, the disintegration of most of the webbing in the winter

revealed that thousands had been deposited on ceiling supports and

Dictyna bellans Chamberlin was also heavily

In addition, at least some of the preponderance of L. sclopetariusin the volumetric webbing might have been due to a sampling artifact. Adults of this species typically spend the daytime resting in

L. sclopetarius were visible in both the volumetric and laminar webbingthroughout the facility. In contrast, the weather was sunny on the

withdrawn from the webbing and quiescent against the adjacent


structural elements. Large specimens of L. sclopetarius in webbingwere only plentiful in the darkness beneath the catwalks of the

Larinioides appressed against the column shafts, such individualswere naturally excluded from the ceiling sheet samples. However,

since juvenile L. sclopetarius may remain in their webs during the

Both types of webbing included one or a few samples containing

maximum ceiling sheet densities of L. sclopetarius and D. bellans webbing in particular varied considerably from place to place, some

samples consisting primarily of apparently newer, cleaner silk and

others packed with the remains of prey and associated dermestid

larvae. However, condition of the webbing was not correlated with

maximum or minimum spider numbers.

In contrast to normalizing the specimen counts as densities,

building by applying these counts to the total estimated amounts of

volumetric and laminar webbing throughout the facility (see previ

Since the amount of volumetric webbing in various locations (Table

1) was so much greater than the ceiling sheet webbing, estimated

T. guatemalensis on a habiT. guatemalensis

DiscussionCommunal Behavior By Solitary Orb-Weaving Spiders. Al

though the construction of a spider web, and particularly an orb

web, has often been regarded as a rigidly constrained series of steps

nological research continues to demonstrate that the process is often

highly plastic and the end result potentially quite variable (Heiling

and Herberstein 2000, 2007). Similarly, despite the frequent generalization of spiders as

coexist with minimal aggression and the blending of web boundaries

of web variability and tolerance for neighbors have repeatedly been

shown to overlap, up to the extremes for both behaviors illustrated

Since increased foraging success appears to be the evolutionary

unsurprising that local prey abundance frequently appears to be the

, Lloyd and Elgar 1997, general correlative rule between prey availability and an individual

that are continually repaired and expanded have been shown to increase web size and/or density when well fed (Roush and Radabaugh

2007), perhaps in part due to an increased ability to allocate more

recycled by ingestion build smaller orbs and/or display a lower

incidence of web construction under conditions of excess prey and

The proximity of neighbors in favorable habitat patches adds

Depending on species and circumstances, close spacing of individuals

silk used indiscriminately by all individuals for prey capture (Gillespie

Table 3. Densities of the 4 most abundant spider species in the Back River Sand Filtration Facility, expressed as numbers of individuals per m3PHDQDQGUDQJHIURPYROXPHWULFDQJHFROXPQVDQGODPLQDU(ceiling sheet) webbing samples. See text for additional details.

Species Volumetric Laminar

Tetragnatha guatemalensis

T. guatemalensis,

Larinioides sclopetarius

Parasteatoda tepidariorum

Dictyna bellans

Table 4. Estimated populations of spiders in the Back River Sand Filtra-WLRQ)DFLOLW\EDVHGRQQXPEHUVRILQGLYLGXDOVIURPYROXPHWULFDQJHcolumns) and laminar (ceiling sheet) webbing samples applied to an estimated 4,162.14 m3 of volumetric webbing and 8,922.42 m2 of laminar webbing. See text for additional details.

Species Volumetric Laminar Total

Tetragnatha guatemalensis

T. guatemalensis,

Larinioides sclopetarius

Parasteatoda tepidariorum

Dictyna bellans

American Entomologist Fall 2010152

as fortuitous aggregations of individuals of solitary species [Uetz

social spider species that either commonly or invariably live in

groups Larinioides and

Tetragnatha are solitary spiders that are frequently abundant nearaquatic habitats such as the margins of rivers and lakes. Larinioidesspp. often attach their webs on anthropogenic structures, particularly

near lights. The adults are nocturnal, constructing simple vertical

orbs with relatively few radii and support strands in the evening,

remaining at the hub until morning, and withdrawing either to the

L. sclopetarius (probably introduced tospider that is strongly associated with water and actively chooses

sites may be occupied by crowded populations of this species, often

framework of an aqueduct revealed that the spiders readily moved

from web to web when disturbed without obviously exhibiting aggressive behaviour to their neighbours (Howes 1999).

ance and collective silk in L. sclopetariusscale from the above observations, involving an enormous, recurring

population on the Riverfront Coliseum Sports Arena in Cincinnati, OH

(now known as the U. S. Bank Arena), apparently as an aggregative

response to abundant prey from the adjacent Ohio River. Densities

of 100 spiders/ mwere observed on masses of webbing that apparently resulted from collapsed orbs and common attachment strands.

The spiders maintained their normal activity cycle, capturing insects

and mating on the communal silk during the night and packing into

A similar example of local hyperabundance of the closely related

L. patagiatus (Clerck) was observed in a power plant wheelhouse,consisting of thousands of juxtaposed webs and an estimated 10,000

to 20,000 spiders of all life stages sharing the webs almost commu

The general range of webbing behavior recorded for Larinioides isparalleled in Tetragnatha, although this much larger and ecologicallymore diverse genus collectively displays an even greater tendency to

deviate from typical orb construction. The latter is usually diagonal

or horizontal and relatively fragile, with some species remaining at

the hub both day and night, and others mainly crepuscular (LeSar

species (T. viridis Walckenaer) does not spin a web (Edwards andEdwards 1997, Aiken and Coyle 2000), while others readily aggregate

T. guatemalensis U.S. records are clustered in Florida and south Texas, and the species

L. sclopetarius, it has largely escaped the attention ofbiologists, with one conspicuous exception. In 2007, a huge expanse

of communal webbing, created mainly by T. guatemalensis (but also

Larinioides sp.) was discovered at Lake Tawakoni State Park in Texas. Consisting of irregular

the giant Texas web quickly became an international media and

Internet sensation, in large part due to compelling photographs of

was formed and enhanced by the cumulative drag lines of wandering

nati L. sclopetariussilk might have been due in part to the repeated construction of typical tetragnathid retreat webbing (Lapp 2007a, b, c). In response to

this event, photographs and descriptions of other uncommonly large,

Although we have only a rudimentary understanding of the

ing spiders in megawebs, these spectacular events may therefore

be less unique than is generally believed. Due to its location in a

modular structure that allowed the extent of its webbing and size

anthropogenic habitats, the Back River aggregation has furnished a

detailed overview of what is by far the most extreme example of its

genre. Combined with previously published accounts, the following

generalizations can be made:

1) Spiders display broad and interrelated spectra of plasticity in

web construction and degree of territoriality, with shared silk and tolerance for neighbors often increasing with high prey density. These

behavioral precedents demonstrate that, despite their potential for

communal constructions are all the more impressive since individual

2) At this point, all published examples of megawebs have been

almost exclusively two species, T. guatemalensis and L. sclopetariussurprisingly, the Lake Tawakoni webbing contained far more taxonomic diversity (at least 21 spider genera in 12 families as reported

by Jackman et al. 2007) than was present at Back River (9 genera in

outdoor habitat. However, whether present due to opportunistic

or inadvertent reasons, it is clear that most of the taxa at both sites

were relatively incidental to the total output of silk. Both the Texas

and Maryland aggregations were similar in that T. guatemalensisaggregations in temperate climates may be substantially larger in

the fall, when Tetragnatha populations typically peak (Williams etfrom severe weather (Lapp 2007a,b).

parian habitat that provided a sustainable reservoir of prey. The vital

link to an aquatic or marine food source has been a prominent focus

in ecological studies of allochthonous nutrient transfer to adjacent

dies including an enormous variety of plants and animals (Polis et

al. 1997). In particular, adult chironomid midges and other emerging

American Entomologist Volume 56, Number 3 153

aquatic insects have been shown to play a dominant role in supplying

nutrition to orb-weaving spiders living on the margins of streams,

rivers, and lakes (Baxter et al. 2005), including L. sclopetarius (Heilingand Herberstein 1998, Heiling 1999) and various Tetragnatha spp.(Williams et al. 1995; Henschel et al. 2001; Collier et al. 2002; Sanzone

et al. 2003; Kato et al. 2003, 2004; Akamatsu 2004). Chironomids

constituted the overwhelming majority of prey in the Back River

web on our sampling date (Fig. 9) and were still heavily swarming

around the facility in mid-December (see discussion below). Both

chironomids and mosquitoes from the adjacent lake and wetlands

appeared to be the principal prey for the Lake Tawakoni aggregation

(Lapp 2007a,b; Jackman et al. 2007; Guarisco 2008).

4) Although individual orbs may persist in a megaweb matrix, the

architecture is characterized by extensive laminar and volumetric

webbing. Various behavioral mechanisms have been proposed to

explain these two types of construction in dense orb-weaver aggre-

gations, but there have been no detailed, long-term studies of their

origin and maintenance. Inasmuch as typical orb webs are famous

as solitary constructs that achieve their purpose with a minimum of

time, energy, and material (Shear 1986, Foelix 1996), it is somewhat

incongruous that species such as L. sclopetarius and T. guatemalensisare capable of collectively producing massive outputs of shared,

three-dimensional silk that are the exact opposite of the spare,

planar, radially-symmetric orbs these spiders create as individuals

in most circumstances. Since taxa that characteristically construct

complex, three-dimensional webs are a relatively recent phylogenetic

development within the orbicularian Araneae (Coddington and Levi

1991, Griswold et al. 1998, Blackledge et al. 2003), the ability of more

basal orb-weavers to organize silk in this manner is a testament to

-sion of web evolution.

Spider Colonization and Hyperabundance In Structural Habi-tats. The prominence of spiders as predictable and persistent inhab-itants of virtually every type of built environment is unmatched by

any other group of predatory arthropods and is a recurring theme of

urban entomology as an ecological discipline. A unique combination

of behavioral and physiological attributes as well as the distinctive

environmental conditions inherent to new, barren ecosystems are

responsible for this success. Of major importance is that spiders as

a group are exceptionally vagile, not just as pedestrians within a local

area but also by the passive mechanisms of anthropochoric transport

and ballooning that potentially result in rapid, long-range dispersal.

Particularly the latter behavior enables them to reliably drift onto

remote islands and the earliest successional substrates created by

Schoener and Toft 1983, Crawford et al. 1995, Polis and Hurd 1995,

Buddle et al. 2000, Hodkinson et al. 2001). Confronted by formidable

rate, conferring a resistance to starvation (Kotiaho 1998), and, in

many cases, low predation pressure and competition for resources

from the relatively few other taxa in these simple systems (Schoener

and Toft 1983, Wise 1993, Polis and Hurd 1995). Buildings present

circumstances similar to most other types of pioneer habitats for

fundamental principles of island biogeography and metapopulation

dynamics as isolated habitat patches in non-anthropogenic environ-

ments (Hanski 1999, Whittaker and Fernndez-Palacios 2007, Losos

and Ricklefs 2010).

In fact, although species at higher trophic levels generally are

more vulnerable to extinction in insularized ecosystems (Holt et al.

1999), structures often represent immense reservoirs of protected

living space for various spider species that are unmatched by any

non-anthropogenic counterpart. Paralleling their wide range of

sociality, spiders also display an equally broad spectrum of synan-

thropy, from occasional, facultative invaders of the built environment

to near-obligate inhabitants that occur practically nowhere else,

particularly in colder climates (Kaston 1983, Edwards and Edwards

1997, Guarisco 1999). At the extreme end of this spectrum are the

refugia and a sustainable and abundant supply of either autochtho-

nous or allochthonous prey are available. Recluse (Loxosceles spp.)and cellar spiders (Pholcidae, particularly Pholcus phalangioides Fuesslin) are often considered as models for achieving remarkably

high densities within typical buildings, exploiting surroundings that

mimic what is assumed to be their original claustral or cavernicolous

habitats (Newlands 1981, Hopkin 1998, Vetter and Barger 2002,

Greene et al. 2009).

spider success due to human construction. By far the largest spider

aggregations in structural environments involve species not normally

associated with secluded building interiors but able to colonize cer-

tain types of facilities that are relatively open to their surroundings

and incorporate, or are in close proximity to, a source of aquatic prey

that exceeds the ability of predators to deplete. The best documented

example of this is a unique series of reports on the unparalleled

density of linyphiid spiders (as high as 67,365 individuals per m3)

1975). The Linyphiidae is a wind-dispersed group of mostly tiny

spiders known as sheet-web weavers that characteristically thrive

in highly disturbed and exposed habitats, and have been shown to

in both agricultural and urban sites (Vanuytven 1986, Shochat et al.

small invertebrate grazers (primarily enchytraeid worms and dip-

as a super habitat in which the life strategy requirements of the

two dominant spider species are maximized and competition from

noted that the numbers of the most abundant of these linyphiids in

its natural marshland communities are never, even remotely, near

exceptional arachnid productivity in a wastewater treatment plant,

albeit with two much larger orb-weaving species, both of which are

habitats. T. guatemalensis, like many other members of its genus, isstrongly associated with the margins of streams, rivers, and lakes,

but not particularly in a structural context (Levi 1981, Dondale et al.

2003). In contrast, the holarctic L. sclopetarius is only rarely observedon vegetation, and is often termed the bridge orb-weaver because it

so commonly occurs on these structures (and other human construc-

1974, Ware and Opell 1989, Heiling and Herberstein 1998, Heiling

1999, Howes 1999, Dondale et al. 2003). It has been suggested that

this distinctive synanthropic preference may be due to the species

original habitat of overhanging river banks that have since been

American Entomologist Fall 2010154

widely eliminated by human engineering (Howes 1999).

Wastewater treatment plants are one category of a wide array of

aquacentric structures that range in size and complexity from mod-

est bridges, docks, and boathouses to giant hydroelectric facilities,

environments that are potentially super habitats for web-building

-vantages over an outdoor site such as the Lake Tawakoni woodland

damaged the Texas web in August shortly after its discovery (Lapp

2007a,b) and undoubtedly acted as a check on its growth through-

out the summer. Some Tetragnatha species are especially sensitiveto rain, strong wind, and low temperatures, and will not construct

webs in these conditions (LeSar and Unzicker 1978, Gillespie and

Caraco 1987).

The buildings second critical asset was that it reliably and con-

tinually generated at least part of its spiders food supply. Enormous

populations of chironomids living in the warm, nutrient-rich water of

sewage treatment plants are well-documented (Gibson 1945, Armit-

abundant in the sand. The water in the facility was about 10 C on

that date, whereas ambient temperatures away from the building

away from the building. Earlier in the winter, on 14 December 09, wa-

ter temperature was about 15 C, ambient temperatures away from

the building averaged about 10 C, and extremely dense clouds of

Therefore, although chironomids that sustain populations of

web-building spiders are almost always an allochthonous input

(Hodkinson et al. 2001, Baxter et al. 2005), the Back River facility was

at least partially self-contained, producing a renewable, autochtho-

nous source of prey. The closed system dynamics clearly extended

to many of the predators as well, since at least the T. guatemalensispopulation appeared to be overwhelmingly renewed from egg sacs

deposited inside the building. In this regard, despite the considerable

-less be considered as fundamentally similar to the subterranean

urban infrastructure that harbors dense populations of Loxosceles rufescens (Dufour) sustained by autochthonous sources of cockroachand termite prey (Greene et al. 2009). Since much of the colonization

of the facility was self-perpetuating and consisted of individuals living

in the location for their entire life cycle, it is questionable whether

the word aggregation (which often implies immigration to a site)

is the most precise terminology for this instance.

It is noteworthy that the Back River plant managers emphasized

those in past years only by degree, and that its operations had never

included the following general points:

1) On-site personnel should be reassured that the spiders are harm-

less and the facilitys immense shroud of silk should be presented

in a positive light as a record-breaking natural history wonder.

2) Pesticides or chemical web-deterrent products, as suggested by

local pest control companies, are unnecessary and inappropriate

in light of the close proximity to treated water.

3) Web and spider removal is basically a recurring custodial func-

tion that should be accomplished by the most feasible mechani-

cal means and on a schedule dependent on the buildup of new

webbing.

4) Lighting of the facility is already minimal, and does not seem to be

a critical factor in attracting additional spiders. However, more

lowering on-site midge populations.

The Back River Arachnotopia (as we referred to it in our edu-

cational material furnished to the plant managers) thus highlights

the utility of aquacentric structures as accessible research sites

where the dynamics of predictable spider hyperabundance can be

closely examined under relatively comfortable conditions. In some

respectsi.e. in its combination of reduced and indirect lighting,

ideal web-attachment surfaces, benign and humid microclimate, and

is a gigantic replica of carefully designed orb-weaver culturing facili-

ties such as the highly successful display of Nephila inaurata Thorellat the National Zoological Park in Washington, D.C. (Robinson and

discipline independent of economic considerations, this type of

to its practitioners.

Acknowledgments

River Wastewater Treatment Plant were extremely generous with

F. Smith for assistance with chironomid taxonomy.

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Al Greene for the Public Buildings Service, U. S. General Services Administration,

Washington, D.C. Jonathan Coddington is a senior research scientist at Nancy L. Breisch is an urban entomologist in the Department of Entomology, Dana De Roche is a museum specialist and research assistant to Jonathan Coddington at the National

Ben Pagac is a medical entomologist working on arthropod-related health issues for the

Department of the Army.

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